The present invention relates to gear synchronizer assemblies, and more particularly to a gear synchronizer mechanism of the type which comprises a gear member rotatable on a transmission shaft, a spline piece formed with a conical portion and integral with the gear member for rotation therewith, a synchronizer ring mounted on the spline piece conical portion and cooperable with the same for providing a cone clutch, a hub member fixed to the shaft, a clutch sleeve encircling the hub member and drivingly connected thereto, the clutch sleeve having an internal splined portion in continual engagement with external splines formed on the hub member and axially shiftable to be engaged with external splines respectively formed on the synchronizer ring and the spline piece, and a plurality of circumferentially equi-spaced strut keys assembled with the inner circumference of the clutch sleeve and loaded radially outwardly into engagement with the clutch sleeve to abut against and urge the synchronizer ring toward the spline piece in shifting operation of the clutch sleeve.
In such a conventional gear synchronizer mechanism as described above, the diameter of the external splines of the synchronizer ring is substantially the same as that of the external splines of the spline piece, and the internal splines of the clutch sleeve are formed in the same construction. In shifting operation of the clutch sleeve, the internal splines of the clutch sleeve are subsequently brought into engagement with the external splines of the synchronizer ring and the external splines of the spline piece. Therefore, the clutch sleeve must be shifted in a relatively long distance corresponding with the sum of the axial length of the external splines on the synchronizer ring, the axial length of the external splines on the spline piece, and the clearances between the clutch sleeve in its neutral position and the synchronizer ring and between the synchronizer ring and the spline piece. For this reason, it is difficult to enhance an operational feel in shift operation of the clutch sleeve. In the conventional gear synchronizer mechanism, it has been experienced that relative rotation between the clutch sleeve and the spline piece increases before the chamfered ends of the internal splines of the clutch sleeve are engaged with the chamfered ends of the external splines of the spline piece after passing through the external splines on the synchronizer ring. This results in occurrence of unpleasant gear noises or unexpected problems in shifting operation.